The present invention relates to a recording apparatus using an electrophotography process, more particularly to a recording apparatus for recording both faces of a recording medium using an electrophotography process.
The present invention relates to a recording apparatus for recording a first face and a second face of a recording medium of a recording paper in which the local uneven deformation in the recording medium due to the local cooling or the local defect in transfer due to the above local uneven deformation in the recording medium can be improved.
The present invention relates to a recording apparatus for recording a first face and a second face of a recording medium of a recording paper in which the local inferiority on the image toners or the local lowering in the density of the image toners can be improved.
A technique of a recording apparatus for recording both faces of the recording paper is proposed, for example in U.S. Pat. No. 4,959,693. This conventional, recording apparatus for recording both faces of the paper comprises a development station for forming non-fixed toner images on the paper (recording medium), a fixing station for heating, fusing and adhering the formed non-fixed toner images on the paper, a reversal station for reversing the paper, and a transportation means for transporting the paper from one station to another next station.
In the first place, after a first face such as a front side of the paper is developed in the development station, the paper is transported toward the fixing station and the paper is fixed in this fixing station. Next, the paper is transported toward the development station, during this paper transportation process the paper goes toward the development station by way of the reversal station in which the paper is reversed in this reversal station.
Next, with the condition in which the paper has been reversed, the development process for a second face such as a back side of the paper is carried out and the paper is fixed in the fixing station similar to the fixing for the first face of the paper and after the fixed paper is discharged from the recording apparatus. As a result, the recording for both faces of the paper is carried out in the conventional recording apparatus.
In the above conventional recording apparatus for recording both faces of the paper, the development station comprises a photosensitive member, a development unit and a transfer unit, and the toner images are formed using an electrophotography process.
In the above transportation means, the conveyor and the pinch rollers etc. are employed as a transportation element. The temperature in the transportation element is lowered less than the temperature in the paper after the first face of the paper has been fixed, and it further works a role of the function for cooling the paper after the first face of the paper has been through the fixing process.
As a heating means used in the fixing station, there are a heat roll fixing method, an oven fixing method and a flash fixing method etc..
In the heat roll fixing method, a fusion sandwiched portion is formed by a heat roll and a backup roll, and the fixing process is carried out on the fusion sandwiched portion by passing through the paper having the non-fixed toner images. In this heat roll fixing method, a paper peeling means is used to peel the paper from the heat roll. As this paper peeling means, there are a claw paper peeling method, an air peeling method for peeling the paper according to the blowing out air etc..
In the paper peeling process, the temperature of the paper peeling element for acting directly on the paper, namely the air and the claw, is lowered less than the temperature in the paper which has been through the fixing process. Also, the temperature of the paper peeling element has the function for cooling the paper.
In the air peeling method, a range for cooling the paper is a range in which the air flows on the face of the paper, generally the range is a portion on the face of the paper. In the conventional air peeling method, as disclosed in U.S. Pat. No. 3,955,813, this conventional recording apparatus has only one nozzle opening of blowing out air.
Further, the air blowing-out direction in the conventional recording apparatus is parallel with the peripheral direction of the heat roll and the air blowing-out direction is the substantially vertical direction with respect to the fusion sandwiched portion of the paper.
Further, the air blowing-out finish timing in the conventional recording apparatus is set at one of the following timings. One above timing is set that at the same time or after a tip portion of the paper is sandwiched by a next transportation means such as a pair of pinch rolls being adjacent to the heat roll. Another above timing is set that at the same time or after the tip portion of the paper is supported by the next transportation means such as a conveyor being adjacent to the heat roll.
Each of the transportation element or the paper peeling element acts on only the portion of the face of the paper. In the present invention, the range in which each of the transportation element or the paper peeling element acts on the face of the paper is called as a "working region" in the present invention.
In the case of the transportation element or the paper peeling claw, the above working region is a range in which the transportation element or the paper peeling claw contacts to the paper. In the case of the air peeling method, the working region is a range in which the air flows on the face of the paper.
Further, when a component necessary for using the air peeling method contacts to the face of the paper, such a contacting region is called the "working region" in the present invention. The above stated many working regions exist on the portions at any one point of the paper.
Besides, since the individual working region exists on the portion of the face of the paper, after the first face of the paper has been through the fixing process, the paper cooling area through the transportation element or the paper peeling element exists locally. However, since the paper cooling portion or region depends on the distribution of the working region, the local paper cooling portion is not limited one portion of the paper, but generally exists on many portions of the paper. This local paper cooling causes the local uneven deformation on the paper.
When after the fixing process for the first face of the paper has been carried out, the paper is transported toward the development station for fixing the second face of the paper leaving the paper having the local uneven deformation, the damage portion in the adhesion characteristic between the paper and the photosensitive member exists locally, and it may cause the defects in transfer on the above damage portion.
In the above stated conventional technique, no considerations are made to the local uneven deformation in the paper caused by the local cooling for the paper due to the transportation element and the peeling element and further the local defects in transfer caused by the above local uneven deformation in the paper. Accordingly, there are problems that the toners suffer local loss or the density in the toners become lower locally.
Further, during the starting time in which the temperature of the transportation element or the peeling element maintains lower, since the cooling degree for the paper is large, the difference in height of the uneven deformation of the paper becomes large, the local defects in transfer occur easily. In particular, during the starting time in the recording apparatus for recording both faces of the paper, there are problems that the degree of the local images defects and the degree of the local density lowering become large, respectively.
In particular, when the first face of the paper has been through the fixing process, many working regions which have been subjected to the cooling exist due to the transportation element, the peeling element and the air for peeling. After the fixing process for the first face of the paper has been carried out, when the second face of the paper is carried through the fixing process, many local defects occur in transfer at many working regions or at many subjected cooling portions on the paper.
In the conventional recording apparatus, a long time for recording both faces of the recording medium and the fixing process for the second face of the recording medium is carried out under the condition in which many working regions in the recording medium remain as they are.
When there is one working region which exists on the recording medium, the operator can hardly notice the defects in transfer on the recording medium. When there are two working regions which exist on the recording medium, the operator can notice dim white portions on the recording medium. These dim white come-out portions show the defects in transfer of the recording medium and all of the toners do not adhere to these dim white come-out portions.
Besides, when there are three working regions which exist on the recording medium, the operator can notice complete white come-out portions on the recording medium. These complete white come-out portions shown the defects in transfer of the recording medium and the toners do not adhere entirely to these complete white come-out portions.
Recently, in the recording apparatus only a short time is required for recording both faces of the recording medium. When the second face of the recording medium is carried through the fixing process, in the conventional recording apparatus it is necessary to carry out such a fixing process under the condition that many working regions remain as they are.